Various sensors have been used for detecting position of an object, such as a stylus or a finger, in a plane. For example, trackpads have become a common form of position detection sensor used with computing devices, such as for providing a digital pointer interface for the user. Such trackpads typically comprise a relatively small rectangular planar sensor surface well suited for integration in portable computers (e.g., laptop computers, notebook computers, personal digital assistants (PDAs), etc.) and other devices (e.g., keyboard assemblies).
The first generation of trackpads was based on local resistive change in the sensor due to pressure of an object touching a sensor surface of the trackpad. An advantage of this technology is that the object for which position is determined (i.e., the object touching the sensor surface, such as a stylus or finger) does not need to be a conductor, such as may accommodate the use of various items as a stylus (e.g., erasure tipped pencil, gloved hand of a user, etc.). However, a disadvantage of this technology is the relatively low sensitivity (e.g., the range of pressure at which object position is detected is small) of the sensor configuration. A further disadvantage of this technology is that an object must be touching a sensing surface of the trackpad, with sufficient pressure, for position to be detected.
The second, current generation of trackpads is based on local change of capacitance due to redistribution of static charge on the touching object. An advantage of this technology is high sensitivity (i.e., sensitivity significantly higher than that of the foregoing first generation trackpads). However, a disadvantage of this technology is that the object used to touch the sensor for position determination must be an electric conductor (e.g., only suitably electrically conductive configurations of stylus, uncovered hand of a user, etc. touching the sensor surface may detected by the sensor).
As can be appreciated from the foregoing, both the first generation trackpad local resistive technology and the second generation local capacitance technology require an object touching a sensor surface for detecting position. Accordingly, neither technology provides for contact-less position detection (i.e., neither technology can trace the position of a collimated light illuminating the sensor surface or of an object hovering above the sensor surface).